Idle Speed Stabilization

The idle speed stabilization system regulates and stabilizes the idle speed. For this purpose an air regulating valve opens a by-pass around the throttle.

A certain opening size is produced depending on activation of the valve. Since the airflow sensor senses this additional air, the injection rate is also changed.

The air regulating valve performs the function of an auxiliary air valve and vacuum control in addition to idle stabilization. The idle speed is also regulated when the A/C clutch is energized. The valve has 2 windings and a limited turning angle of approximately 90°.

Input information (position of idle contact, engine temperature and engine speed) are processed in the LH fuel control unit. From the LH fuel control unit the air regulating valve receives a cycled voltage signal, which acts on both windings alternately during a positioning period. This produces opposing rotating forces on the armature. Due to the nature of the armature, the valve is set to a certain angle, which is equal to the duty cycle of the applied voltage.

With changes in the input signals and change in engine speed, the duty cycle for the valve also changes. A programmed nominal speed is compared with the actual speed in control unit. Airflow rate is then changed by valve until nominal and actual speeds are the same. Nominal speed of a warm engine is approximately 690 RPM.